When certain fruits or vegetables are harvested, especially underground vegetables such as potatoes or the like, the harvesting machinery is likely to include significant quantities of dirt clods and/or rocks in with the desired product. It then becomes necessary to separate the desired product from the undesired dirt, rocks or other debris.
This separation can be accomplished manually, by having workers pick the vegetables out from the debris as they pass by on a conveyor. In order to eliminate this hard, tedious manual labor, a number of machines have been devised over the years. Feller, U.S. Pat. No. 4,375,853, issued in 1983, contains a description of the prior art in this field, and presents one of the better solutions to the problem.
In Feller's '853 device, the mixture of desired product (potatoes) and undesired debris (dirt clods) is conveyed to a free-fall area, where it falls onto a rotating steel roller. The components of the mixture bounce off the roller in varying degrees, depending on the characteristics of the individual components. Obviously, potatoes bounce more than dirt. This separates the stream of mixed material into two streams, which can then be collected separately. This device has the drawback, however, that bouncing off a steel roller can bruise the product. If one is harvesting potatoes to be dried or powdered, this does not matter, but if one is interested in preserving the fruit or vegetable involved for sale as whole product it becomes important to avoid bruising as much as possible.
Feller's later U.S. Pat. No. 4,744,470, issued in 1988, is a refinement of the '853 patent, with the intention of improving separation of rocks from the potatoes. In the '470 patent, Feller discloses the use of a rebound surface which absorbs more kinetic energy from hard objects, such as rocks, and less from soft objects, such as potatoes. One embodiment (FIG. 3) shows a roller which has a steel core covered with a thin layer of foam, with an impact surface made of a plurality of stainless steel rings. This variation on the original Feller device does little or nothing to minimize the bruising of the product, as can be seen in column 2, lines 41-45: ". . . the impact surface is stiff enough to be generally unaffected by the impact thereon of softer agricultural products, which rebound therefrom, as from a rigid surface."